Conventionally, in order to reduce energy required for fixing a toner, a toner with excellent low temperature fixing property is developed. To improve the low temperature fixing property of the toner, it is necessary to lower a glass transition temperature (Tg) of a binder resin in the toner. However, if the glass transition temperature of the binder resin is lowered, preservation and storage property of the toner is deteriorated. Thus, if practicality of the toner is considered, the glass transition temperature can only be lowered to about 50 degrees centigrade.
A toner particle with a capsule structure (core-shell structure) is proposed as a module which maintains the fine preservation and storage property of the toner while the glass transition temperature of the binder resin is lowered. The capsule structure refers to a structure formed by a binder resin that has a low glass transition temperature at the inside (core) of the toner particle and has a high glass transition temperature at the outside (shell) of the toner particle.
In a fusion process where a binder resin for shell is fused into a binder resin for core, it is necessary to fully adhere the core and the shell to make the surface of the toner particle with the capsule structure uniformly smooth. However, in the fusion process, as the core and the shell are partially mixed, it is difficult to form an ideal capsule structure in the toner particle. That is, it is difficult to obtain a toner with both the low temperature fixing property and the preservation and storage property.